1. Field of the Invention
The present invention relates to a black level correction circuit used for a solid-state imaging device and the like, and particularly relates to a clamp circuit correcting blocked up shadows.
2. Description of the Related Art
In a clamp circuit, a black level is maintained to be constant normally by detecting the difference with respect to a target value and feeding back the difference to a DAC (digital-analog converter) section. However, at the time of the detection, there are a case where there are many points having obviously higher level than a target black level in a level in which removal of white points is not performed and a case where part of patterns such as a frame is included in a calculation range. In such cases, the black level in a clamp range becomes higher than the black level in an effective pixel region, which increases a control value to the DAC section more than necessary.
As a result, excessive drawing is performed, and when the black level is displayed in 8-bit (0 to 255), values in the black level which can be originally outputted are fixed to “0”, which results in so-called blocked up shadows.
In view of the above, when the black level is fixed to “0”, it becomes necessary to check causes and consider the countermeasures, then, to take action such as circuit correction in related art.
In JP-A-2007-059991 (Patent Document 1), an ADC (analog-digital converter) and a DAC (digital-analog converter) in a solid-state imaging device are disclosed, however, a feedback circuit for correcting blocked up shadows is not disclosed. In JP-A-2006-222708 (Patent Document 2), a correction circuit for blocked up shadows in a MOS image sensor mounted on a cellular phone is disclosed, however, there is no description about digital processing for correcting the black level in the feedback circuit and gain switching for adjusting the feedback amount.